Object-Oriented Software Engineering Practical Software Development using UML and Java. Chapter 1: Software and Software Engineering

Transcription

1 Object-Oriented Software Engineering Practical Software Development using UML and Java Chapter 1: Software and Software Engineering

2 1.1 The Nature of Software... Software is intangible Hard to understand development effort Software is easy to reproduce Cost is in its development in other engineering products, manufacturing is the costly stage The industry is labor-intensive Hard to automate Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 2

3 The Nature of Software... Untrained people can hack something together Quality problems are hard to notice Software is easy to modify People make changes without fully understanding it Software does not wear out It deteriorates by having its design changed: erroneously, or in ways that were not anticipated, thus making it complex Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 3

4 The Nature of Software Conclusions Much software has poor design and is getting worse Demand for software is high and rising We are in a perpetual software crisis We have to learn to engineer software Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 4

5 Types of Software... Custom For a specific customer Generic Sold on open market Often called COTS (Commercial Off The Shelf) Shrink-wrapped Embedded Built into hardware Hard to change Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 5

6 Types of Software Differences among custom, generic and embedded software Custom Generic Embedded Number of copies in use low medium high Total processing power devoted to running this type of software Worldwide annual development effort low high medium high medium low Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 6

7 Types of Software Real time software E.g. control and monitoring systems Must react immediately Safety often a concern Data processing software Used to run businesses Accuracy and security of data are key Some software has both aspects Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 7

8 1.2 What is Software Engineering?... The process of solving customers problems by the systematic development and evolution of large, highquality software systems within cost, time and other constraints Solving customers problems This is the goal of software engineering Sometimes the solution is to buy, not build Adding unnecessary features does not help solve the problem Software engineers must communicate effectively to identify and understand the problem Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 8

9 What is Software Engineering? Systematic development and evolution An engineering process involves applying well understood techniques in a organized and disciplined way Many well-accepted practices have been formally standardized e.g. by the IEEE or ISO Most development work is evolution Large, high quality software systems Software engineering techniques are needed because large systems cannot be completely understood by one person Teamwork and co-ordination are required Key challenge: Dividing up the work and ensuring that the parts of the system work properly together The end-product that is produced must be of sufficient quality Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 9

10 What is Software Engineering? Cost, time and other constraints Finite resources The benefit must outweigh the cost Others are competing to do the job cheaper and faster Inaccurate estimates of cost and time have caused many project failures Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 10

11 1.3 Software Engineering and the Engineering Profession The term Software Engineering was coined in 1968 People began to realize that the principles of engineering should be applied to software development Engineering is a licensed profession In order to protect the public Engineers design artifacts following well accepted practices which involve the application of science, mathematics and economics Ethical practice is also a key tenet of the profession Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 11

12 1.4 Stakeholders in Software Engineering 1. Users Those who use the software 2. Customers Those who pay for the software 3. Software developers 4. Development Managers All four roles can be fulfilled by the same person Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 12

13 1.5 Software Quality... Usability Users can learn it and fast and get their job done easily Efficiency It doesn t waste resources such as CPU time and memory Reliability It does what it is required to do without failing Maintainability It can be easily changed Reusability Its parts can be used in other projects, so reprogramming is not needed Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 13

14 Software Quality... Customer: solves problems at an acceptable cost in terms of money paid and resources used User: easy to learn; efficient to use; helps get work done QUALITY SOFTWARE Developer: easy to design; easy to maintain; easy to reuse its parts Development manager: sells more and pleases customers while costing less to develop and maintain Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 14

15 Software Quality The different qualities can conflict Increasing efficiency can reduce maintainability or reusability Increasing usability can reduce efficiency Setting objectives for quality is a key engineering activity You then design to meet the objectives Avoids over-engineering which wastes money Optimizing is also sometimes necessary E.g. obtain the highest possible reliability using a fixed budget Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 15

16 Internal Quality Criteria These: Characterize aspects of the design of the software Have an effect on the external quality attributes E.g. The amount of commenting of the code The complexity of the code Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 16

17 Short Term Vs. Long Term Quality Short term: Does the software meet the customer s immediate needs? Is it sufficiently efficient for the volume of data we have today? Long term: Maintainability Customer s future needs Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 17

18 1.6 Software Engineering Projects Most projects are evolutionary or maintenance projects, involving work on legacy systems Corrective projects: fixing defects Adaptive projects: changing the system in response to changes in Operating system Database Rules and regulations Enhancement projects: adding new features for users Reengineering or perfective projects: changing the system internally so it is more maintainable Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 18

19 Software Engineering Projects Green field projects New development The minority of projects Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 19

20 Software Engineering Projects Projects that involve building on a framework or a set of existing components. The framework is an application that is missing some important details. E.g. Specific rules of this organization. Such projects: Involve plugging together components that are: - Already developed. - Provide significant functionality. Benefit from reusing reliable software. Provide much of the same freedom to innovate found in green field development. Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 20

21 1.7 Activities Common to Software Projects... Requirements and specification Includes Domain analysis Defining the problem Requirements gathering - Obtaining input from as many sources as possible Requirements analysis - Organizing the information Requirements specification - Writing detailed instructions about how the software should behave Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 21

22 Activities Common to Software Projects... Design Deciding how the requirements should be implemented, using the available technology Includes: Systems engineering: Deciding what should be in hardware and what in software Software architecture: Dividing the system into subsystems and deciding how the subsystems will interact Detailed design of the internals of a subsystem User interface design Design of databases Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 22

23 Activities Common to Software Projects Modeling Creating representations of the domain or the software Use case modeling Structural modeling Dynamic and behavioural modeling Programming Quality assurance Reviews and inspections Testing Deployment Managing the process Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 23

24 1.8 The Eight Themes of the Book 1. Understanding the customer and the user 2. Basing development on solid principles and reusable technology 3. Object orientation 4. Visual modeling using UML 5. Evaluation of alternatives 6. Iterative development 7. Communicating effectively using documentation 8. Risk management in all SE activities Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 24

25 1.9 Difficulties and Risks in Software Engineering Complexity and large numbers of details Uncertainty about technology Uncertainty about requirements Uncertainty about software engineering skills Constant change Deterioration of software design Political risks Lethbridge/Laganière 2001 Chapter 1: Software and Software Engineering 25